Early service loss or failure indication in an unlicensed mobile access network

ABSTRACT

An Unlicensed Mobile Access Network Controller (UNC) and method for providing an early indication of service failure to a mobile station registered with the UNC. When the UNC detects a network failure that prevents service to the mobile station, the UNC prohibits new registrations by other mobile stations, starts a timer, and monitors the network failure to determine if the failure clears. If the failure clears before the timer expires, new registrations are accepted from other mobile stations. However, if the timer expires before the failure clears, the UNC continues to prohibit new registrations from other mobile stations, and deregisters the mobile station when a network Keep Alive timer expires for the mobile station. When a plurality of mobile stations are registered with the UNC, the UNC deregisters the plurality of mobile stations one at a time as the network Keep Alive timer expires for each mobile station.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to radio telecommunication systems. Inparticular, and not by way of limitation, the invention is directed to asystem and method for providing a mobile user with an early indicationof service loss or service failure in an Unlicensed Mobile AccessNetwork (UMAN).

DESCRIPTION OF RELATED ART

In a traditional cellular system, such as the Global System for MobileCommunications (GSM), a malfunctioning interface from the Base StationController (BSC) towards the mobile core network, or malfunctioninginternal resources in the BSC, are not signaled towards a mobile station(MS) until the MS attempts a layer 3 procedure such as attempting tomake a call. Likewise, the prevention of service is not detected untilthe MS attempts a layer 3 procedure whenever a network node, for examplethe BSC or Mobile Switching Center (MSC), is working at a high load andtherefore would reject an access attempt. The prevention of service isnot detected earlier because the MS is only listening to the informationbroadcast from base stations in the network, and this information doesnot change in response to changes in the core network status. Therefore,unless the core network indicates an overload situation to the radioaccess network, the mobile station may select and lock onto an accessnetwork that is unusable.

It would be advantageous to have a system and method that overcomes thedisadvantages of the existing methodology by providing an earlyindication of service loss or service failure to the MS. The presentinvention provides such a system and method.

SUMMARY OF THE INVENTION

The present invention is a system and method for providing a mobile userwith an early indication of service loss or service failure in anUnlicensed Mobile Access Network (UMAN).

Thus in one aspect, the present invention is directed to a method ofproviding an early indication of service failure to a mobile stationregistered with an Unlicensed Mobile Access Network Controller (UNC).The method is performed within the UNC and comprises the steps ofdetecting a network failure that prevents service to the mobile station;determining whether the failure is a short term failure or a persistentfailure; and upon determining that the failure is a persistent failure,deregistering the mobile station. The failure may be determined as ashort term failure or a persistent failure by starting a timer when thenetwork failure is detected, and determining that the failure is a shortterm failure if the failure is corrected before the timer expires. Themethod may also prohibit new registrations by other mobile stationsduring the time period after the failure is detected and before thefailure is corrected.

In another aspect, the present invention is directed to a method ofproviding an early indication of service failure to a mobile stationregistered with a UNC. The method is performed within the UNC andcomprises the steps of detecting a network failure that prevents serviceto the mobile station, and upon detecting the network failure,prohibiting new registrations by other mobile stations and starting atimer. The network failure is then monitored to determine if the failureclears. If the failure clears before the timer expires, newregistrations are accepted from other mobile stations. However, if thetimer expires before the failure clears, the UNC continues to prohibitnew registrations from other mobile stations, and deregisters the mobilestation when a network Keep Alive timer expires for the mobile station.When a plurality of mobile stations are registered with the UNC, themethod includes the step of deregistering the plurality of mobilestations one at a time as the network Keep Alive timer expires for eachmobile station.

In yet another aspect, the present invention is directed to a UNC forproviding an early indication of service failure to a mobile stationregistered with the UNC. The UNC includes means for detecting a networkfailure that prevents service to the mobile station; means fordetermining whether the failure is a short term failure or a persistentfailure; and means responsive to a determination that the failure is apersistent failure, for deregistering the mobile station. Afterdetecting the network failure, the UNC may prohibit new registrationsfrom other mobile stations until the failure clears. When a plurality ofmobile stations are registered with the UNC, the UNC deregisters theplurality of mobile stations one at a time as the network Keep Alivetimer expires for each mobile station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an unlicensed-radio accessnetwork and a conventional cellular mobile communications networksuitable for implementing the present invention;

FIG. 2 is a signaling diagram illustrating the flow of signalingmessages in a first exemplary embodiment of the present invention; and

FIG. 3 is a flow chart illustrating the steps of an embodiment of themethod of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Unlicensed Mobile Access (UMA) technology utilizes an unlicensed radioband to support mobile telecommunication systems operating in licensedradio bands. For example, the Unlicensed Radio service may support GSMcircuit-switched services and GSM Packet Radio Service (GPRS)packet-switched services. Access may be provided over unlicensedspectrum technologies such as Bluetooth or Wireless Local Area Network(WLAN) 802.11.

The unlicensed-radio access network enables MSs to communicate with thecore network portion of a conventional mobile communications network,such as a GSM network, via an unlicensed-radio interface. The term“unlicensed-radio” means any radio protocol that does not require theoperator running the mobile network to have obtained a license from theappropriate regulatory body. In general, such unlicensed-radiotechnologies must be low power and thus of limited range compared tolicensed mobile radio services. A benefit of this lower power is thatthe battery lifetime of mobile stations is greater. Moreover, becausethe range is limited the unlicensed-radio may be a broadband radio, thusproviding improved voice quality. The radio interface may utilize anysuitable unlicensed-radio protocol, for example a wireless LAN protocol,Digital Enhanced Cordless Telecommunications (DECT), or Bluetooth radio.

When a traditional cellular system is extended with other accessmethods, such as unlicensed radio access networks, uninterruptedservices can be provided to the end user (the MS) even if severeproblems occur in the core mobile network or in the interface betweenthe unlicensed mobile access network controller (UNC) and the corenetwork. Also since broadband Internet Protocol (IP) networks are usedbetween the access point and the UNC, malfunctions in the IP network orin the voice gateways (used to convert voice/IP to normal Time DivisionMultiplexed (TDM) signaling that is used towards the core mobilenetworks) may be detected and should influence which access network theMS uses.

FIG. 1 is a simplified block diagram of an unlicensed-radio accessnetwork and a conventional cellular mobile communications networksuitable for implementing the present invention. In an unlicensed radioaccess network an interface node is needed to aggregate and interconnectto the core mobile network. From the core network point of view, thisnode is seen as a traditional access network controller node. This typeof node is referred to herein as a Home Base Station Controller (HBSC)or Unlicensed Mobile Access Network Controller (UNC) to distinguish itfrom the traditional cellular system.

In the exemplary embodiment illustrated in FIG. 1, a UMA-enabled,dual-mode mobile station (MS) 11 is operating within the coverage areaof a GSM Base Station Subsystem (BSS) 12, which may include a BaseTransceiver Station (BTS) 13, a transmission network 14, and a BaseStation Controller (BSC) 15. The BSC interfaces with a core mobilenetwork 16, which may include a Home Location Register (HLR) 17, aMobile Switching Center (MSC) 18, a Visitor Location Register (VLR) 19,and a Serving GPRS Service Node (SGSN) 20. The MS may also access aBluetooth piconet 21 over an unlicensed radio frequency. The Bluetoothpiconet provides access to the core mobile network through an AccessPoint (AP), which may be any Bluetooth or 802.11 WLAN access point. InFIG. 1, the AP is a Home Base Station (HBS) 22. The HBS communicatesthrough a broadband access network 23 and a UNC 24, which interfaceswith the core mobile network 16. The broadband access network may be anytype of access network that can carry IP traffic (for example, xDSL,CATV, Ethernet, and the like).

With new alternate access networks that are based on unreliable,unmanaged IP networks, however, there is a need for methods andprocedures to control that the mobiles are offered availability as highas that offered by the Cellular network. For this to be the case, thenetwork should have the ability to force the MS to use other accessnetwork in case of problems or faults in currently used access network.

In one embodiment of the present invention, the UNC 24 follows thefollowing procedures. If the A-interface (GSM) or Iu interface (WCDMA)towards the core mobile network 16 fails, this indicates a seriousfault. For example, it may indicate that the MSC 18 has failed,transmission failed, signaling terminals failed, or the like. When theUNC detects this condition, the UNC starts a timer to filterintermittent faults. While the timer is running, no new mobiles areallowed to connect to or register with the UNC. If the fault clearsbefore the timer expires, it was an intermittent fault, andregistrations are again accepted. However, if the fault conditionremains after the expiration of the timer, the UNC starts to disconnectMSs currently registered and served by the UNC in order to force the MSsto use another access network. The UNC may also start redirecting theMSs to other access networks, for example to other UNCs.

The UNC 24 performs the same actions when conditions prevail that wouldprevent successful calls/services, for example in case all voicegateway/media gateway resources are lost, the interface to the SGSN 20is down, or other internal faults exist. Similar procedures may also beapplied in case the UNC is overloaded or has received an indication thatthe core mobile network 16 is overloaded. In this case, the UNC mayeither disconnect/redirect MSs until the overload condition ceases, ormay disconnect/redirect MSs when they attempt a layer 3 procedure, andthe overload condition still exists. The MS may then connect to a UNCthat is less loaded or to a UNC that is connected to a MSC that is lessloaded. If no alternative UNC/MSC is found, the MS may attach to thecellular network.

In UMA networks, all MSs register at the UNC, thereby creating an MScontext that remains in the UNC until the MS is either deregistered bythe UNC, roved out (e.g., roam out or walk-away), or redirected toanother UNC. When a failure is detected, the UNC should deregister orredirect the MSs as early as possible so that the MSs is deregistered orredirected before the MS actively tries to make a call and detects thatservice is unavailable.

The number of registered MSs in a UNC can be up to tens or hundreds ofthousands, so de-registrations and redirections need to be distributedover time so that the GSM core network is not overloaded with a largenumber of Location Updates at the same time (if the UNC and alternativeGERAN network belong to different Location Areas).

FIG. 2 is a signaling diagram illustrating the signaling messagesbetween the MS 11 and the UNC 24 when performing a Network ControlledKeep Alive procedure. All MSs registered with the UNC 24 perform theKeep Alive procedure. At step 31, a Transmission Control Protocol (TCP)connection is established through the broadband access network 23(FIG. 1) between the MS and the UNC. At step 32, the MS sends aRegistration Request message to the UNC. At step 33, the UNC returns aRegistration Accept message to the MS, and then starts a Keep Alivesupervision timer at 34 for this particular MS. The Registration Acceptmessage includes a predefined time interval for setting an MS Keep Alivetimer. When the MS receives the Registration Accept message, the MSstarts its Keep Alive timer at step 35 and sets the timer for theinterval defined in the Registration Accept message. Each registered MSperiodically sends a Keep Alive message to the UNC at a predefinedinterval such as every 10 minutes. Therefore, when the MS Keep Alivetimer is triggered at 36, the MS sends a Keep Alive message to the UNCat 37, and restarts the MS Keep Alive timer. The UNC supervises thereceipt of Keep Alive messages, and if a Keep Alive message is notreceived from a particular MS, the UNC may deregister the MS.

FIG. 3 is a flow chart illustrating the steps of an embodiment of themethod of the present invention. At step 41, the MS 11 registers withthe UNC 24. At step 42, the UNC detects a fault or system failure thatprevents service for the MSs that are registered with the UNC. At step43, the UNC starts a filtering timer to determine whether the fault isan intermittent fault or a persistent fault. At step 44, the UNCprohibits all new registrations from MSs while the filtering timer isrunning. At step 45, the UNC determines whether the fault has cleared.If so, the fault was an intermittent fault, and the method moves to step46 where the UNC resumes accepting registrations from MSs. However, ifthe fault has not cleared at step 45, the method moves to step 47 wherethe UNC determines whether the filtering timer has expired. If not, themethod returns to step 44 where the UNC continues to prohibit new MSregistrations.

However, if the filtering timer has expired, and the fault has notcleared, the fault is a persistent fault, and the method moves to step48 where the UNC begins to deregister (or redirect) the registered MSsusing the Keep Alive supervision timer in the UNC to distribute thede-registrations in time. Thus, the UNC does not deregister all MSs atonce. Instead, the UNC waits for the network Keep Alive supervisiontimer to trigger for each MS. The network Keep Alive timer triggers at adifferent time for each MS because the network Keep Alive timer isinitiated for each MS when the MS initially registers with the UNC.

After the MS is deregistered, the method moves to step 49 where the MSmay search and find another access network such as a GSM EDGE RadioAccess Network (GERAN), or the MS may be redirected to another UNC,based on fault type and operator policy.

The description above has been mainly focusing on the UMA case. The sameprinciple is also applicable for licensed mobile networks such as GERANand WCDMA networks. The main difference is that in these mobilenetworks, there is no idle mode context in the radio access networks forMSs using these cells. Therefore, when the radio access networkcontroller (e.g. BSC or RNC) detects faults that would prevent servicefor the MSs, the controller may indicate in the broadcast systeminformation that the current cell is bad, and the MS should search foranother cell. Examples of the system information that could be usedinclude an indication in the Access Control Class bits that MSsbelonging to a specific Access Class are not allowed to access the cell.This information may also be used in the UMA case. Alternatively, thesystem information may indicate that the cell is barred, or may indicatein the Cell Selection parameters (e.g. CELL-RESELECT-HYSTERESIS or RXLEVACCESS-MIN) that the MS should not select the current cell. Finally, theBSC or RNC may simply turn off the Broadcast Control Channel (BCCH)making the whole cell ‘disappear’.

Those skilled in the art will readily appreciate that the presentinvention may be implemented using either hardware, or software, orboth, and further, software implementations may vary using differentlanguages and data structures. The present invention is not limited to aspecific language and/or class of languages, nor is it limited to anysingle data structure implantation.

The present invention may of course, be carried out in other specificways than those herein set forth without departing from the essentialcharacteristics of the invention. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

1. A method of providing an early indication of service failure to amobile station registered with an Unlicensed Mobile Access NetworkController (UNC), said method being performed within the UNC andcomprising the steps of: detecting a network failure that preventsservice to the mobile station; determining whether the failure is ashort term failure or a persistent failure; and upon determining thatthe failure is a persistent failure, deregistering the mobile station.2. The method of claim 1, wherein the step of determining whether thefailure is a short term failure or a persistent failure includes thesteps of: starting a timer when the network failure is detected; anddetermining that the failure is a short term failure if the failure iscorrected before the timer expires.
 3. The method of claim 2, furthercomprising prohibiting new registrations by mobile stations during atime period after the failure is detected and before the failure iscorrected.
 4. The method of claim 3, further comprising accepting newregistrations by mobile stations if the timer has not expired and thefailure has been corrected.
 5. The method of claim 1, wherein the stepof deregistering the mobile station includes deregistering the mobilestation when a network Keep Alive timer expires for the mobile station.6. The method of claim 1, wherein a plurality of mobile stations areregistered with the UNC1 and the step of deregistering the mobilestation includes deregistering the plurality of mobile stations one at atime over a period of time.
 7. The method of claim 6, wherein the stepof deregistering the plurality of mobile stations one at a time over aperiod of time includes deregistering each mobile station when a networkKeep Alive timer expires for each mobile station.
 8. The method of claim1, further comprising redirecting the deregistered mobile station toanother access network.
 9. A method of providing an early indication ofservice failure to a mobile station registered with an Unlicensed MobileAccess Network Controller (UNC), said method being performed within theUNC and comprising the steps of: detecting a network failure thatprevents service to the mobile station; upon detecting the networkfailure: prohibiting new registrations by other mobile stations; andstarting a timer; monitoring the network failure to determine if thefailure clears; if the failure clears before the timer expires,accepting new registrations by mobile stations; if the timer expiresbefore the failure clears; continuing to prohibit new registrations byother mobile stations; and deregistering the mobile station when anetwork Keep Alive timer expires for the mobile station.
 10. The methodof claim 9, wherein a plurality of mobile stations are registered withthe UNC, and the step of deregistering the mobile station includesderegistering the plurality of mobile stations one at a time as thenetwork Keep Alive timer expires for each mobile station.
 11. The methodof claim 9, further comprising redirecting the deregistered mobilestation to another access network.
 12. An Unlicensed Mobile AccessNetwork Controller (UNC) for providing an early indication of servicefailure to a mobile station registered with the UNC, said UNCcomprising: means for detecting a network failure that prevents serviceto the mobile station; means for determining whether the failure is ashort term failure or a persistent Failure; and means responsive to adetermination that the failure is a persistent failure, forderegistering the mobile station.
 13. The UNC of claim 12, wherein themeans for determining whether the failure is a short term failure or apersistent failure includes: a timer for measuring a filtering timeperiod, said timer being started when the network failure is detected;means for monitoring the network failure to determine if the failureclears; and means for determining that the failure is a short termfailure if the failure clears before the filtering time period expires.14. The UNC of claim 13, further comprising means for prohibiting newregistrations by mobile stations during a time period after the failureis detected and before the failure is corrected.
 15. The UNC of claim14, further comprising means for accepting new registrations by mobilestations if the timer has not expired and the failure has beencorrected.
 16. The UNC of claim 12, wherein the means for deregisteringthe mobile station includes: a network Keep Alive timer that measures aKeep Alive time period for each mobile station registered with the UNC;and means for deregistering the mobile station when the network KeepAlive timer expires for the mobile station.
 17. The UNC of claim 12,wherein a plurality of mobile stations are registered with the UNC1 andthe means for deregistering the mobile station includes means forderegistering the plurality of mobile stations one at a time over aperiod of time.
 18. The UNC of claim 17, wherein the means forderegistering the plurality of mobile stations one at a time over aperiod of time includes: a network Keep Alive timer that measures a KeepAlive time period for each mobile station registered with the UNC; andmeans for deregistering each mobile station when the network Keep Alivetimer expires for each mobile station.
 19. The UNC of claim 1, furthercomprising means for redirecting the deregistered mobile station toanother access network.